The objective of this study is to determine the intracellular location of the structural changes thought to occur during temporary hearing loss following exposure to loud noise. Noise- induced hearing loss is a very common medical problem in our society. This study will contribute to the medical community's knowledge of the basic cellular mechanism involved in noise-induced deafness. Such knowledge will undoubtedly be useful in the prevention of permanent deafness resulting from repeated episodes of temporary hearing loss. The specific aims of this proposal are to answer the following questions about the structural changes within hair cells that are suffering from noise-induced temporary threshold shift. Are the sensory hairs (stereocilia) altered by apical constriction, or are the extracellular fibers which connect and support adjacent hairs changed during the period of temporary deafness. Such alterations could reduce the sound-induced movement of the stereocilia to decrease damage from overstimulation. Are there structural changes in the synaptic end of the hair cells, such as a decrease in the number of synaptic vesicles or an accumulation of abnormal large vacuoles which could be a sign of synaptic fatigue. Do the hair cells recover from these structural changes on the same time scale as they recover from the temporary deafness, indicating a close coupling of the structural and functional changes during temporary hearing loss.